Formaldehyde an Oxidation Product of Chlorophyll Extracts. 379 



formaldehyde, but it is very important that the possibility of the observed 

 effects being due to some other aldehyde or to a mixture of aldehydes should 

 be borne in mind. This point still requires investigation. 



The Production of Formaldehyde by Chlcrrophyll Extracts in Air. 



In 14 experiments films of chlorophyll extract together with tubes of soda 

 water were exposed to light in glass jars with well-fitting stoppers greased 

 with vaseline. The effect both of electric light (eight experiments) and 

 sunlight (six experiments) was investigated. In the former case the source 

 consisted usually of one or two 32 c.p. filament lamps which were separated 

 from the vessels containing the films by a glass tank, 2 inches thick, 

 through which cold water flowed ; the exposures varied from 6 to 70 hours.* 

 The films illuminated by sunlight were exposed outside a south window for 

 periods ranging from two and a. quarter hours of bright sunshine to seven 

 days bright at intervals (March 4-11, 1913). 



Similar films were always exposed in jars containing tubes of potassium 

 hydroxide solution. These control films were allowed to stand in the dark 

 in vacuo over lime for several days before being rapidly placed in the jars, 

 and then for several more days over the potash solution before exposure to 

 light. In all the films a development of formaldehyde was observed, the 

 solutions becoming very decidedly coloured in most instances when the test 

 was applied. In 10 of these experiments no difference could be detected 

 between the amounts of aldehyde formed in the presence of carbon dioxide 

 and in its absence. In three there was a very slight excess in the films 

 exposed to carbon dioxide as compared with the control films, but the 

 difference was so small as to be barely perceptible, while in the remaining 

 experiment slightly more aldehyde was found in the film which had not 

 been exposed to carbon dioxide. 



Subsequently three experiments were carried out with somewhat greater 

 precautions, sealed glass tubes replacing the stoppered jars throughout. 

 The exposures varied from one to two and a half hours of bright summer 

 sunshine, and in each case the production of formaldehyde was very evident. 

 In one instance it was impossible to distinguish between the amounts 

 formed in the presence and absence of carbon dioxide, while in the other 

 two there was slightly more formaldehyde produced in the films which had 

 been exposed over potash solution. In all of the 17 experiments control 

 . films were also examined which had remained in the dark for equal periods, 



* During the daytime these films received diffuse sunlight in addition to artificial 

 light. 



VOL. LXXXVII. — B. 2 F 



